Will, you are asking some interesting questions.
I have MRL test tapes for speeds down to 1.88 and
if I use off-speed transfers, I transfer the MRL
as well. You can also use it (or the calcs at the
MRL site) to adjust the equalization. If you
can't get it flat at the reproducer, you can make
a "flattening" curve in the DAW and add that to what the machine equalizes.
That will get you flat to today's standards. If
you KNOW the standards in place at the time, then
you can do mods from the modern standard to make
up for that. If you don't know the historic
standards, I suggest using the closest actual
standard and EQing from there to taste in the
post production process. Why? Because if y ou
later find out the historic standard and you
transferred to a known standard, you can apply the correction factor.
The good news is that slow-speed recording has
been pretty standard over the years in both Europe and North America.
Oh, and I'd use a narrower head than full-track
as my experience is that at 7.5 in/s some tapes
that were recorded full track will have enough
dimensional shift to comb-filter the high
frequencies as the azimuth wanders. If the tape
plays well with a full-track head then I'd do it,
as that will provide best reproduction, but if
you can get a 100-mil centre swath, that might be the best.
Look at the MRL site for the historic EQs as
well. Start with his Choosing and Using document.
I think you'll find that the NAB standard for
3.75 propagated around the world so anything that
was copied from any flavour of Western technology
should be to that standard. 1.88 might be less of
a standard, but from reel-to-reel tapes be happy
if you get anything approaching fidelity. I think
even Tandberg set an upper limit of 8kHz for
their response at 1.88. It was only later that
Nakamichi (and others) showed us the way.
The other option MIGHT be direct/constant current
recording as in instrumentation recorders. Again,
if you find that out later, you can convert.
I don't think 1.88 and 3.75 in/s recordings made
on consumer recorders from 1953-1965 are going to
be particularly high fidelity, and from 1965-1991
they might be, but towards the end I suspect
quality will fall off again as the recording
equipment aged. I've done a few tapes where the
family kept the same machine for a 15 year period
and the later recordings sounded worse than the earlier ones.
I would try to get documented transfers and then
fix whatever you can in post. I would suspect a
lot of 50 Hz hum that will be unstable due to
speed perturbations in the recorder.
This is all speculation, but it is also process.
Use it as you see fit. We still don't know the
precise EQ curve of Mullin's modified
Magnetophons, so we're transferring at the 17.5
Ás EQ curve spec'd for today's 30 in/s
reproduction. If we ever find out, we'll modify
what we need to. If anything goes out, it can be adjusted now to sound "good."
Tape Restoration Seminar: MAY 9-12, 2006; details at Web site.
Richard L. Hess email: [log in to unmask]
Aurora, Ontario, Canada (905) 713 6733 1-877-TAPE-FIX
Detailed contact information: http://www.richardhess.com/tape/contact.htm